1. Field of the Invention
The present invention relates to a light wavelength converter, which is used in an information processor, such as an optical memory disc system or a laser beam printer, and an optical application measuring apparatus using laser beams emitted from a semiconductor laser device when the wavelength of the laser beams is converted into a short wavelength zone.
2. Description of the Prior Art
For an information processor, such as an optical memory disc system or a laser beam printer, and an optical application measuring apparatus, the laser beam of a semiconductor device that is superior in condense property and directivity is used. In general, the oscillation wavelength of semiconductor laser devices is 0.78 .mu.m or 0.83 .mu.m, the laser beam being near infrared. In recent years, in order to increase the amount of information to be processed in an information processor, or to improve the measurement accuracy of the optical application measuring apparatus, the laser beam has been promoted to be of a short wavelength. For example, in the information processor, such as an optical memory disc system or laser beam printer, the laser beam emitted from the semiconductor laser is condensed at a predetermined place so as to write the information or images. The wavelength of the laser beam and the diameter of focusing spot usually have therebetween a proportional relationship, so that, when the wavelength of laser beam becomes short, the diameter of focusing spot can be reduced. When the diameter thereof is reduced, the amount of information (i.e., the recording density) to be written into the optical memory disc system can be increased. Moreover, the laser beam printer can form micro-images, so that the recording density can be increased and the resolution can be improved. Furthermore, the optical application measuring apparatus reduces the wavelength of the laser beam to enable an improvement in measuring accuracy. The green or blue laser beam of a short wavelength, when obtainable with ease, is combined with the red laser beam now in use, thereby attaining a color operating at high speed and having a high resolution.
In recent years, a semiconductor laser has been developed which uses a semiconductor material of the InGaA1P system and has an oscillating wavelength of about 0.6 .mu.m. However, a semiconductor laser which can oscillate a green or blue laser beam with an oscillation wavelength of less than 0.6 .mu.m has not been manufactured because suitable materials are not to be found. For that reason, such a green or blue short wavelength laser beam must be oscillated by a large-scale gas laser such as an argon-ion laser.
To obtain a green or blue short wavelength laser beam without using such a large-scale gas laser, a light wavelength converter for converting into a short wavelength zone a laser beam oscillated from a solid laser or a semiconductor laser has been proposed by Ohta et al. in the Institute of Applied Physics in spring, 1984. This light wavelength converter utilizes the second harmonic generation (SHG) phenomenon caused by a crystal that attains the optical nonlinear effect and outputs a laser beam of half of the wavelength of the input laser beam. The said light wavelength converter is provided with, as shown in FIG. 7, an optical waveguide 72 that is formed into a plate on a Z-plate LiNbO.sub.3 substrate by a Ti diffusion technique. On the optical waveguide 72, a Luneberg lens 73 formed by vacuum deposition of As.sub.2 S.sub.3 and a coupler prism 74 are disposed. The coupler prism 74 guides into the optical waveguide 72 a pair of laser beams 75 (the optical frequency of which is represented by .omega.) oscillated from, for example, a YAG laser, the laser beams 75 being propagated in the optical waveguide 72. Each waveguiding light 75' propagated in the optical waveguide 72 is refracted so as to intersect with each other. Each waveguiding light 75' is converted at the intersection into a second harmonic light 76 with twice the optical frequency (i.e., half of the wavelength) of the laser beam 75 when a phase matching condition of each waveguiding light 75' is satisfied. The phase matching condition is as follows: EQU 2.beta..sup..omega. cos .theta.=.beta..sup.2 .omega.,
Where in .beta..sup..omega. is the propagation constant of a fundamental wave (the light guided into the optical waveguide, .beta..sup.2 .omega. is the propagation constant of the second harmonic light, and 2 .theta. is the intersection angle at the intersection between the waveguiding lights.
In the light wavelength converter, the changes of the intersection angle of waveguiding lights 75' by means of the Luneberg lens 73 are carried out by mechanically changing the interval between the pair of laser beams 75, the interval between both the laser beams 75 being so adjusted that the above-mentioned phase matching condition is satisfied.
As mentioned above, in such a conventional light wavelength converter, the interval between a pair of incident laser beams are adjusted and the phase matching condition is satisfied, thereby oscillating the second harmonic light. However, the propagation constant .beta..sup..omega. of the fundamental wave and the .beta..sup.2.omega. of the second harmonic light change in a sensitive manner with small changes in ambient temperature, whereby it is difficult to quickly adjust the interval between the laser beams incident into the optical waveguide corresponding to the changes in the ambient temperature, so that the phase matching condition cannot be satisfied in a proper response. As a result, the optical intensity of the second harmonic light decreases.
The light wavelength converter forms a optical waveguide at a substrate composed of material having the optical non-linear effect, so that a pair of waveguiding lights propagating in the optical waveguide are intersected to generate the second harmonic light, the converter having light deflection means for changing the direction of each waveguiding light on the basis of an electric signal, thereby attaining the above-mentioned object.